Physical Properties of Oxygen Molecule
Oxygen with atomic number 8 and symbol ‘O’ is the most abundant chemical element occurrence in group-16 or chalcogen groups in the periodic table uses to makes up 47% of the earth crust in the form of liquid and solid oxides, oxoacids, and oxygen gas. The natural oxygen atom is an isotopic mixture of O-16, O-17, and O-18 isotopes that occur in the natural environment 21% by volume in air and 86% by weight of liquid water in oceans and essential for animal respiration system. O-17 and O-18 prepared by fractional distillation or electrolysis of water or thermal diffusion of oxygen gas molecule. O-18 isotope uses as the tracer in kinetics and mechanistic studies but O-17 uses in NMR spectrum analysis.
In learning chemistry, the outermost quantum shell consists of the 2s2 2p3 electronic configuration. Oxygen alone in the group-16 or chalcogen group does not possess and d-orbital. Therefore, oxygen only shows valency 2. But due to the presence of vacant d-orbitals other elements like sulfur, selenium, tellurium, and polonium posses 2, 4. and 6 valances for chemical bonding purposes.
Chemical Properties Oxygen Atom
The ionization energy of oxygen is very high among the group-16 element. Therefore the metallic character is very low and well known as a nonmetal. With the increasing atomic number in group-16, the resistance of the elements decreases. Therefore, oxygen and sulfur are an insulator, selenium and tellurium are semiconductors but polonium is a metal conductor of electrical energy. Due to 2s2 2p4 outer electronic configuration, oxygen always shows -2 oxidation number or state.
The elements are two electrons short of the next noble gas configuration. Therefore, when bonding with other these two electrons achieved by gaining two electrons by electropositive elements or by making two single covalent bonds or one double bond with other elements. Hence oxygen has very high electronegativity and electron affinity favor for the formation of crystalline solid with alkali and alkaline earth metals.
Chemical Properties Oxygen Gas
Oxygen occurs in two allotropic forms like dioxygen and ozone. The colorless orderless oxygen molecule is paramagnetic in nature with two unpaired electrons and pale blue in liquid state but blue in the crystal lattice. Dioxygen is fairly soluble in water and highly soluble in organic solvents like acetone and benzene and forms weak charge-transfer complexes.
In the ground state, the highest occupied molecular orbitals have two electrons with the parallel spin in two pi-antibonding orbitals. It is said to the triplet state. But the next higher state, one in which the electrons are spin paired in pi-antibonding molecular orbitals. Therefore, these states termed as singlet states. Normally a triplet to singlet transition forbidden. Therefore, the gaseous O2-molecule colorless. But in liquid or solid oxygen, a single photon collides with other molecules and excite both. Absorption of electromagnetic spectrum radiation in the red region to the green visible region gives observed blue color.
Isolation of Chemical Element O2
Oxygen element or gas molecule obtained industrially by fractional distillation of liquid air. In the laboratory, it may be prepared by,
- Catalytic decomposition of hydrogen peroxide over the platinum catalyst in nickel foil.
- Thermal decomposition of potassium chlorate. The reaction occurs at 400° to 500°C. If we use manganese dioxide as a catalyst, the reaction occurs at 150°C. But this process also produces 3% of ClO2.
2KClO3 → 2KCl + O2
- Thermal decomposition of pure potassium permanganate in a vacuum at specific heat gives very pure O2-molecule.
2KMnO4 → K2MnO4 + MnO2 + O2
Uses in Chemical Industry
Oxygen is the third chemical in order of use in the industry after sulfuric acid and nitrogen. Nearly 100 million tones beings consumed annually throughout the world. Therefore, it largely used in metallurgy like steel making in blast furnaces and Bessemer converters. It also used in direct oxidation in many chemical processes. For making synthesis gas and oxidizing of organic hydrocarbon like methane, ethane, ethylene, etc. Oxygen gas molecule in chemistry uses as an oxidizer for the fuels in rocket propulsion.